I have tendonitis (like so many), and while I don't get the pain so much the big issues I get are fretting hand fatigue, weakness and lack of dexterity. It comes and goes (depending on if something has exacerbated it). Some years ago, my job was more physical, and I noticed on days where I did stuff like stacking servers or printers a bunch, I could come home and just SHRED the guitar. Somehow the strenuous activity 'pumped up' my hand/forearm muscles and my fretting hand was stronger, didn't tire and I had great dexterity. Only lasted that day. I'd wake up the next morning and everything would be back to how it was. Short of keeping a couple of pallets of printers or servers in my living room for a daily stacking regimen, any suggestions on how I could build hand strength and keep them fit? What do you guys do to keep your hands in shape?